1. Field of the Invention
The present invention relates generally to communications networking, and more specifically, to modulating bandwidth in a communications network.
2. Related Art
Conventional cable communications systems deploy a cable modem headend that manages communications with a plurality of cable modems. The headend defines the upstream operating characteristics that enable the cable modems to send carrier signals upstream to the headend. The upstream may consist of multiple channels that can be assigned to the cable modems. These channels are separated from each other by operating at different frequencies.
One or more cable modems use a designated frequency channel to transmit a carrier signal carrying requests and/or data to the headend. The headend receives the upstream signal at a demodulator that interfaces with the physical spectrum interconnecting the cable modems with the headend (i.e., demodulator). The demodulator recovers the underlying requests and/or grants from the carrier signal and forwards this information to a media access controller (MAC) for additional processing.
A headend demodulator conventionally allows a single “channel” to be received from the physical spectrum of a physical plant (such as, a hybrid fiber-coaxial cable plant). In other words, if the upstream consists of multiple channels, a separate demodulator must be coupled to the headend MAC to receive each channel. Therefore, the headend establishes the operating characteristics of each physical spectrum of a physical plant (e.g., HFC plant) to allow a single channel to be received at a single demodulator. Although the physical spectra can be partitioned into channels that are separated from each other by frequency, the center frequency and symbol rate for each channel must be defined in such a way that the channel's spectrum does not overlap (or minimally overlaps in a way that can be corrected with equalization) the spectra of other channels on the same physical plant.
In other words, if the headend communicates with cable modems requiring differing operating characteristics (e.g., center frequency, symbol rates, modulation standards, etc.), a separate demodulator must be provided for each of the separate channels having different operating characteristics. Similarly, if one cable modem uses time division multiple access (TDMA) modulation to send upstream bursts in a TDMA minislot, and a second cable modem uses code division multiple access (CDMA) modulation to send upstream bursts in a CDMA frame, a separate demodulator must be provided to interface with the CDMA and TDMA channels.
Therefore, a protocol for managing upstream properties is needed to address the above problems.